1. Field of the Invention
The present invention generally relates to a three-dimensional measuring device and a board inspection device equipped with this three-dimensional measuring device.
2. Background Art
Generally, a printed circuit board is provided with an electrode pattern on a base substrate formed from glass-filled epoxy resin, and the printed circuit board is protected by a surface resist film. When an electronic component is mounted on this printed circuit board, cream solder is first printed on positions lacking protection by the resist film on the electrode pattern. Thereafter, the electronic component is temporarily fixed on the printed circuit board by use of the viscosity of this cream solder. Thereafter, this printed circuit board is placed in a reflow furnace, and the printed circuit board is subjected to a certain reflow step in order to perform soldering. There recently has been a need for inspection of the printed state of the cream solder prior to the printed circuit board being carried to the reflow furnace, and a three-dimensional measuring device is sometimes used during such inspection.
Various proposals have been made in recent years for three-dimensional measuring devices which use light, e.g., so-called non-contacting type three-dimensional measuring devices. For example, a three-dimensional measuring device using the phase shift method illuminates the object (e.g., printed circuit board) using a visible light source having a light pattern having a stripped light intensity distribution. Then, the object is imaged by a CCD camera. The phase differentials of the fringes of this light pattern are analyzed using the obtained image, and the three-dimensional shape, especially height, of the cream solder is measured.
However, various colors (e.g., background regions) are present within the range of the printed part of the cream solder on the printed circuit board. Such colors are due to the use of various colors for the glass epoxy resin and the resin film. This results in low contrast in the image data based on imaging by the CCD camera at a background region having a comparatively dark color (e.g., black). That is, the contrast of this light pattern (brightness difference) becomes small. Therefore, measurement of the brightness of the background region may become difficult. Standardization of heights within the board has previously been desirable for highly accurate measurement of the height of cream solder printed on the board. However, due to the inability to appropriately use the background region as a surface of standard height, it may be difficult to standardize height within the board.
Thus, technology has been proposed (see e.g., Japanese Patent Application Publication No. 2006-300539: JP2006-300539) for appropriate measurement of the height standard by performing separate imaging, for example, at an exposure time (e.g., 10 milliseconds (ms)) appropriate for the solder printing region (bright part) and at a different exposure time (e.g., 50 ms) for the background region (dark part).
Technology has also been proposed (see e.g., Japanese Patent Application Publication No. H7-50786: JPH7-50786) for increasing dynamic range by taking multiple images at exposure times (e.g., 10 ms each) such that the brightness of a pixel within the area corresponding to the bright part of the object is not saturated and by then summing the obtained multiple imaging data.
However, when imaging is performed separately for the solder printing region (bright part) and for the background region (dark part) as in JP2006-300539, a comparatively long time is required for obtaining all the required image data for performing three-dimensional measurement of a certain measurement object area (image area).
In a situation that the optimum exposure time for measurement of the solder printing region is 10 ms, the optimum exposure time for measurement of the height standard is 50 ms, and the time required for data transmission of each image data is 16 ms, the configuration of Patent Application Publication No. 2006-300539 requires a total time equal to 10 ms imaging time for the solder printing region+16 ms data transmission time+50 ms imaging time for the background region+16 ms data transmission time=92 ms.
Also, a great increase in the number of imaging operations occurs, as per JPH7-50786, by multiple imaging operations using exposure times such that brightness saturation does not occur for pixels within an area corresponding to the bright part of the measurement object. Thus, under assumed conditions similar to those described previously, a further prolonged time is required, e.g., total of 5 images (each having a 10 ms imaging time+a 16 ms data transmission time)=130 ms.
The time required for measurement of a single printed circuit board is further increased several fold when multiple measurement object areas (imaging areas) are established on the single printed circuit board or when 3 or 4 imaging operations are required for a single three-dimensional measurement using the phase shift method or the like.